Holography has been used widely for the generation of diffraction gratings (U.S. Pat. No. 3,578,845) and three-dimensional images of objects and scenes (U.S. Pat. Nos. 3,506,327; 3,580,655; 3,758,186). To make a diffraction grating, the interference pattern formed by the interference between two or more mutually coherent optical wavefronts (usually one spherical or planar wavefront and another spherical, cylindrical, or planar wavefront) is recorded on a high-resolution optical recording medium, such as a Lippman emulsion, photopolymer, photoresist, or dichromated gelatin. Such gratings are used in spectrophotometers, heads-up displays, and other optical instruments.
To make a three-dimensional image, the interference pattern formed by the interference between a spherical or planar wavefront and a complex wavefront formed by the reflection of coherent light from the surface of an object (or by transmission of coherent light through an object) is recorded on a high-resolution photographic medium. Alternatively, a three-dimensional image may be synthesized as described in U.S. Pat. No. 4,206,965 by recording a large number of two-dimensional views of an object, in which case each individual recording step usually involves only the interference between a spherical or planar reference wavefront and a spherical, planar, or other wavefront carrying a two-dimensional image.
An improved form of holography to record threedimensional images, described in U.S. Pat. No. 3,633,989, reduces or eliminates all vertical parallax and thereby allows unblurred reconstruction with a white light source. As a consequence, the image appears in nearly pure spectral colors. Later extensions of the technique have included multiple images, each with different recording conditions to produce multicolored, three-dimensional images.
Radially symmetric, mechanically ruled diffraction gratings, especially spiral gratings, have been used to provide decorative color effects. Segments of spiral gratings have been joined to form diffractive mosaic patterns. These gratings and grating mosaics have been generated as surface relief patterns and have been replicated by thermoplastic embossing. The embossed grating mosaics have been used as substrates for printed graphics.
In some instances, simple, holographically generated diffraction gratings have been replicated by embossing and used as decorative material. In such instances, the diffraction gratings have been limited to low-frequency, very simple, nonrandom patterns incapable of providing the types of effects provided by the methods disclosed herein, such as selected arbitrary textural effects, predetermined uniform color effects, and the illustion of motion.